Last week a team from the Product Stewardship Institute took a tour of a materials recovery facility (MRF; pronounced “murph”) operated by Casella Waste Systems in Charlestown, Massachusetts, which recycles material from municipalities in the Boston area. We would like to thank Lisa McMenemy, the Municipal Development Representative at Casella, for being such an informative tour guide and leading us through all the steps of the recycling process. The Charlestown MRF was converted to a single-stream (also known as Zero-Sort or fully-comingled) facility in 2009. The concept of single stream comes from Europe and is widely believed to dramatically increase the recycling rate because of the added convenience for consumers, although the quality of the materials recovered is lower. Single-stream allows for recyclable materials (such as cardboard, newspaper, aluminum cans, plastic bottles, and glass containers) to all be placed in the same bin. When we are so accustomed to ease of curbside collection and other convenient methods of recycling, it’s hard to imagine how complex process actually is.
The single-stream MRF that PSI visited was highly automated and use cutting edge technology in order to separate materials. The Charlestown MRF recycles around 750 tons of material every day and the most common material that is recycled is newspaper, which accounts for 60% of all the materials that are processed at the Charlestown site. The inflows of recyclable materials are highly seasonal, with some of the largest fluctuations coinciding around the holiday season and also university events such as graduations and moving days.
The first step in the recycling process is taken when trucks deliver loads of recyclable material to the MRF. The materials are dumped in large piles, which are then pushed onto conveyer belts by bobcats (also known as skid steers). Metering chains make sure that the materials are not stacked too high and will not encumber the sorting processs.
With all the materials spread out along the conveyer belt, the pre-sorting begins. The pre-sort is a labor-intensive step where materials that are not recyclable, or that may damage the equipment, are removed by hand. Plastic bags are by far the biggest contaminant in the recycling process, and are not able to be recycled once they get to the MRF. It is important to remember that even if you have good intentions and wish to recycle your grocery bags, the bags can slip through the pre-sort and end up in bales of other material. If a bale reaches a certain level of contamination, it can be rejected by a mill and must then be reprocessed, which requires additional energy, recycling time, and money. Everyone should reuse plastic bags as much as possible, and consider purchasing a durable canvas bag for shopping needs. If you want to recycle the plastic bags accumulating in your household, bring them to a store that collects them and don’t put them in your recycling bin or they willbecome a contaminant. There are national retailers offering collection programs across the country. Lowe’s and Target both offer complimentary recycling stations for plastic bags and you should be sure to check with you local grocer or retailer to see if they offer similar services as well.
With the pre-sort complete, a series of screens then separates out light paper products, such as newspaper, from heavier products that will fall through the screens and move onto a further series of conveyer belts. The smallest objects, typically broken glass and shredded bits of paper, falls through the screen and sent to a belt beneath the entire system of screens, while the plastics and metals continue on.
Next, magnetic fields are used to force metal cans from the main conveyer belt. A magnetic current is calibrated so that steal and tin products are separated into one bunker, and a reverse magnetic field is used to so aluminum products are separated into another bunker.
Now that paper and metals have been removed from the conveyer belt, plastics are further separated by their physical properties. An optical sorter separates clear plastics, such as soda bottles, from opaque plastics, such as milk jugs. When the optical sorter identifies a material as a certain type of plastic, different forces of compressed air are shot at the conveyer belt and are adjusted to propel separate types of plastics into separate containers.
Once all the materials are sorted they are separated into bales that are sold to mills in order to be reprocessed into familiar products. Just a few examples of new products created from recycled materials are plastic bottles that will be converted into carpet and fleece, tin cans that will become rebar and bike parts, and cardboard which will be reclaimed as a lower grade of paper product such as cereal boxes. It is important to recycle as much as you can in order to create great products out of used materials, but it is important not to recycle material that may contaminate loads. Don’t hesitate to call your local waste management service provider to determine what materials are acceptable in your area. For those covered by Casella’s service you may visit http://www.casella.com/what-we-do/who-we-serve/town for more information.